The present invention relates to a pneumatic vehicle tire, especially for commercial vehicles, with circumferential wave-shaped grooves whereby the amplitude of the waveshape at the bottom of the groove is substantially greater than at the periphery of the tread and whereby the increase of the amplitude with increasing tread depth is continuous. Such a pneumatic vehicle tire is known from U.S. Pat. No. 3,055,410. This embodiment of the prior art is designed to prevent so-called retention of stones in the grooves.
In this context, "retention of stones" refers to the property of treaded vehicle tires to retain stones in the grooves. This property is detrimental to the performance of the tire, because, when of a considerable size, such retained stones may damage the bottom of the grooves. With pneumatic vehicle tires, with which the present invention is concerned, such retained stones may penetrate the tire tread and reach the reinforcement belt layers. By doing so, a capillary is formed through which moisture may come into contact with the steel wire cord and corrode the reinforcement belt layers. This not only results in a reduction of the wire stiffness, but also especially in a reduction of the adhesion of the polymer or rubber to the metal. Furthermore, retained stones may be ejected like a projectile from the tread surface when the tire is rotated at high enough speeds. The retained stones also cause an untrue run of the tires.
Although this prior art patent provides a certain reduction of the detrimental retention of stones, a large number of stones is still retained.
From Austrian patent 325971 as well as from German Offenlegungschrift 21 57 814 a tire tread with meander-like wound longitudinal grooves is known in which a center section arranged between the meander extremes is essentially extending in an axial direction. This arrangement extends continuously from the bottom of the groove to the periphery of the tread, where it improves the transmission of longitudinal forces within the tread periphery (braking, acceleration). However, both treads which are designed for mud and snow tires do not reduce the retention of stones.
The problem of retention of stones is greater for commercial vehicle tires than for tires for passenger cars or motorcycles because the required service life or mileage is substantially greater for commercial vehicle tires. At the same time, the tire diameter is greater while the maximum speed that is commonly reached is lower. Accordingly, the maximum centrifugal force, which acts on the stones that have penetrated the tire tread and which may cause the ejection of the stones, is substantially smaller for commercial tires than for passenger car or motorcycle tires. Furthermore, the problem of retention of stones is worsened by respective operational conditions where the tires are in contact with a plurality of stones. Thus, this problem is especially prevalent for trailer tires of construction vehicles.
Furthermore, the problem of stone retention is especially pronounced for a tire embodiments according to European patent 0 173 101 because the tires according to this document exhibit a very high service life due to a reduction of the rolling resistance resulting from the temperature reduction accomplished within the tire tread.
It is therefore an object of the present invention to provide a tire tread for a pneumatic vehicle tire with which the retention of stones may be reduced.